Effect of ammonium salts on the properties of poly(piperazineamide) thin film composite nanofiltration membrane

Interfacial polymerization (IP) is most commonly used to fabricate thin film composite (TFC) nanofiltration (NF) membranes. The separation performance of the top thin film layer is affected by many factors such as type of monomers, surfactant, and reaction time during the IP process. This paper presents a systematic investigation on the effect of ammonium salts added in aqueous phase. Six amine salts with different molecular structures, molecular weights and size, including symmetrical and asymmetrical cationic amine group were incorporated into piperazine (PIP) solution. The formed piperazine-amide (PA) polymer layer was supported on a polyethersulfone (PES) ultrafiltation (UF) membrane. The membranes were characterized by scanning electronic microscopy (SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and atomic force microscopy (AFM). The permeate and rejections of NaCl and MgSO4 were also evaluated. The NaCl rejection changed from 27.7% to 46%. It was found that ammonium salt acted as a catalyst during the IP process, transporting multi-amine monomer molecular into organic solution. It also indicated that the ammonium salt containing larger-size steric configuration cationic amine group could result in a better performance and a rougher surface. The solubility and water sorption properties of ammonium salt in organic solution are supposed to play a significant effect on membrane performance.